Chemoelectric cell

ABSTRACT

A chemoelectric cell includes positive and negative electrodes which are spaced to define an interspace therebetween containing electrolyte fluid. At least one of the electrodes is a gas electrode. An electrochemically active substance in the gaseous state is delivered to the interspace so that the interspace serves as both a gas space and an electrolyte space.

This is a continuation of application Ser. No. 696,925, filed June 17,1976 now abandoned.

BACKGROUND AND OBJECTS

The present invention refers to a chemoelectric cell containing apositive electrode and a negative electrode with electrolyte disposed inthe interspace between the two electrodes, whereby at least oneelectrode is a gas electrode, with means for supply and discharge of anelectrochemically active substance in the gaseous state.

Gas diffusion electrodes are used in many new electrochemical powersources, for instance metal air cells, methanol air cells, differenttypes of fuel cells, etc. One side of the gas diffusion electrode is incontact with a gas phase (for instance the air space in a metal air cellor the hydrogen space in a hydrogen air cell) and the other side isexposed to an electrolyte phase which, in turn, is in contact with theother electrode in the actual chemoelectric cell (for instance the metalanode in a metal air cell).

Gas diffusion electrodes are used also in chemoelectric cells forelectrolysis, for instance electrolytic cells for the production ofchlorine and alkali. The present invention can also be used with suchchemoelectric cells.

The nomenclature in this field is not very clear. In this description"gas electrode" means a complete electrode for electrochemical reactionof the substance which is supplied in the gaseous state to theelectrode. The active part of the gas electrode where theelectrochemical reactions are taking place in simultaneous contactbetween the electrode material, the electrolyte, and the gas, is hereincalled "gas diffusion electrode." The gas diffusion electrode is, ingeneral, porous and contains therefore most often a gas phase, anelectrolyte phase, and the solid electrode material.

The gas electrodes according to the present state of art exhibit, aswill be demonstrated in some detail below, quite difficult designproblems when it comes to achieving sufficient mechanical stability andassuring supply of gas and electronic conduction. The gas electrodestherefore occupy a much larger volume than what is dictated by theelectrocatalytic function which, in turn, requires but very smallamounts of catalysts, which in general occupy a very small part of thevolume of the gas electrode.

The present invention involves a completely new design of gas electrodeswhich permit a sizable reduction of the volume requirements of the gaselectrode. A number of other advantages are also obtained, like greatersimplicity and a more robust mechanical design, which is of greatimportance, for instance in tractionary applications. I shall, to beginwith, describe the invention using a metal air battery as an example. Iwill also give examples of hydrogen air batteries and electrolytic cellsaccording to the invention.

Comparison between an alkaline iron air cell and an alkaline iron nickelcell of conventional design shows that the positive nickel oxideelectrode in the conventional alkaline accumulator corresponds to theair electrode, which in this case comprises two gas diffusion electrodesand the air space between them. One advantage with the iron air cellcompared to the iron nickel cell is, of course, that any active materialneed not be stored in the air electrode, which is fed with the oxygen ofthe air, whereas the positive nickel oxide electrode must contain allthe active positive material for the electrochemical processes. Thisactive material represents important weight, volume, and costs factorsat large capacities. Material usage, volume requirement, and weight forconventional air electrodes are, however, not negligible items as wasindicated above. The cathode cost is frequently a dominating item in thematerial calculus for iron air cells.

It is an object of the present invention to eliminate or minimizeproblems of the herebefore encountered.

It is another object to provide a novel electrochemical cell.

BRIEF DESCRIPTION

The present invention constitutes a new step in the development of thiskind of power source which is in principle of the same importance as thestep from the conventional positive nickel oxide electrode to the airelectrode of the type described above. The principle of the inventioncan be described most easily in the following way. Gas is supplied tothe gas diffusion electrode from the electrolyte side instead of from aspecial gas room on the other side of the gas diffusion electrode ascharacterized by the known state of the art. Mass transfer to and fromthe electrode material is therefore taking place from the very sameelectrode side. If the two sides of the gas diffusion electrode areutilized in this way a gas electrode according to the invention willconsist of a single electrode instead of two electrodes with an airspace in between. The gas is brought into contact with theelectrocatalytically active electrode material from the electrolyteside. The gas space and the electrolyte space has, so to say, beencombined in the interspace which was formerly used solely for theelectrolyte according to the known state of the art. It is immediatelyrecognized that the new principle gives several advantages.

The mechanical stresses are reduced since the electrode, according tothe invention, does not have to take a differential pressure. Materialusage is, of course, reduced to a large extent as well as weight andvolume. The most surprising thing is, however, that good electrochemicalperformance can be obtained with gas electrodes according to theinvention. The characteristic feature of the cell according to theinvention is that the means for the supply of the electrochemicallyactive substance in gaseous state is disposed so as to supply thisgaseous substance in the interspace between the electrodes, whereby theinterspace simultaneously serves as a gas and electrolyte space.

A particularly advantageous embodiment is that the gas electrode surfacewhich is exposed to the interspace is at least partly covered with alayer which is permeable to the gas and hydrophobic to the electrolyte.

THE DRAWINGS

Other characteristic features and advantages of the invention willbecome apparent from the following description of preferred embodimentsof the cell according to the invention, which description will refer tothe drawing wherein:

FIG. 1 shows a metal air battery according to the prior state of theart;

FIG. 2 shows a hydrogen air battery according to the prior state of theart;

FIG. 3 shows a chlor alkali electrolyzer with air cathodes according tothe prior state of the art;

FIG. 4 shows an alkali electrolyzer with hydrogen anode according to theprior state of the art;

FIG. 5 shows an alkali electrolyzer with hydrogen anode and air cathodeaccording to the prior state of the art;

FIG. 6 shows an embodiment of a battery according to the invention;

FIG. 7 shows an embodiment of an air cathode according to the inventionas seen from one of the interspaces between the electrodes in a battery;

FIGS. 8A-8C show alternate patterns for the cathode surface according toFIG. 7;

FIG. 9 shows a cross section of a cell according to the invention withseparate channels for gas and electrolyte disposed in the interspacebetween the electrodes;

FIGS. 10-12 show variations of the channels according to FIG. 9;

FIG. 13 shows a so-called air respirating metal air cell according tothe invention;

FIGS. 14-15 show a cylindrical iron air battery according to theinvention;

FIG. 16 shows a chlor alkali electrolyzer with air cathode according tothe invention;

FIG. 17 shows an alkali electrolyzer with hydrogen anode according tothe invention;

FIG. 18 shows an alkali electrolyzer with an hydrogen anode as well asan air cathode according to the invention.

DETAILED DESCRIPTION

The state of the art is thus exemplified by structures comprising ametal air battery, FIG. 1, a hydrogen air battery, FIG. 2, and differentkinds of electrolytic cells, FIGS. 3-5.

Prior Art

For simplicity the following example will refer to batteries built inpile shape as has been described in the Swedish Pat. No. 349,189 and theSwedish Pat. No. 217,054.

Metal air batteries frequently consist of a pile of air electrodes 1 andelectrolyte spaces 2 arranged between them, and metal anodes 3 as shownin FIG. 1. Methanol air batteries can also be built in the same way withan electro-catalytically active methanol electrode for oxidation ofmethanol, which is supplied with electrolyte, instead of the ironelectrode. FIG. 1 shows, in the same principal way, the design of ahydrogen metal oxide battery, for instance a hydrogen nickel batterywith, in this case, the hydrogen electrode 1 and the metal oxideelectrode 3.

The hydrogen air battery according to FIG. 2 contains air electrodes 4and hydrogen electrodes 5. These batteries are, of course, furnishedwith current conductors, pole bolts, channels for supply and dischargeof electrolyte and gases, separators, etc which are required for theoperation of the battery, which components, however, are not shown inthe figure.

Gas electrodes, for instance air electrodes or hydrogen electrodesaccording to the state of the art are framed in a plastic frame 7, whichare connected so as to form a gas space 8 between the two electrodes.The gas electrode frequently also contains channels for the supply anddischarge of the gas in question.

Air electrodes for metal air batteries, FIG. 1, are frequently of theso-called bi-functional type, which means that they can take charge withoxygen evolution with no damage to the catalytic function for thereduction of oxygen during discharge. Bi-functional air electrodesfrequently consist of a finer layer 9 which is filled with electrolyteand which is exposed to the electrolyte, and a coarser layer 10containing catalysts for the reduction of oxygen which is exposed to theair space and which is partly filled with air during normal operation.The so-called two-layer electrodes are also used in fuel cells, wherebythe fine layer prevents gas leakage to the electrolyte space. The stateof art in the field of gas diffusion electrodes is described in atreatise by H. A. Liebhafsky and E. J. Cairns entitled Fuel Cells andFuel Batteries, published by John Wiley & Sons, New York, 1968.

The chlor alkali cell according to FIG. 3 contains a diaphragm 11 whichseparates the electrolyte space in a catholyte space 12 and an anolytespace 13. Hydrogen is developed at the cathode 14 during simultaneousformation of alkali in the catholyte space, where chlorine gas isdeveloped at the chlorine electrode 15.

The chlorine electrode 15 has, in FIG. 4, been exchanged for a hydrogenelectrode 16 with a gas space 17, which space is supplied with hydrogenduring the simultaneous formation of hydrochloric acid in the anolytespace.

In FIG. 5 the cathode 14 of FIG. 3 has been replaced with an air cathode18 comprising an electrode 19 and a gas space 20 which is supplied withair. There will be no hydrogen evolution at the cathode in this case. Onthe contrary, the oxygen of the air is reduced during the simultaneousformation of alkali in the catholyte space. Hydrochloric acid is formedin the room 13 at the oxidation of the hydrogen gas which is supplied tothe anode 16 in the same way as in FIG. 4.

FIGS. 3-5 show only the basic principles of the cell concepts inquestion. The figures have therefore not been provided with known andnecessary means for the supply of electric current and reactants as wellas discharge of reaction products. The state of the art as welldescribed for instance in Encyclopedia of Chemical Technology, 2nd Ed,Volume 1, pages 668-707, by Kirk-Othmer.

Present Invention

FIG. 6 shows, in principle, a preferred embodiment of the presentinvention involving an iron air battery with bi-polar electrodes. Onegreat advantage with the invention is that it makes possible the simpleand rational design of bi-polar metal gas electrodes, for instancebi-polar iron air or zinc chlor electrodes.

The battery pile in FIG. 6 is built-up of elements 21 consisting of aplastic frame 22 containing bi-polar iron air electrodes including aporous iron layer 23 disposed on a separating wall 24 of nickel-coatediron which wall is electrically conducting and which carries theelectrode material 25 of the air electrode on its other side. Theelectrolyte, in this example 5-N KOH, is supplied to interspace 28 bymeans of the channel system 26 and is discharged via overflow 27according to the Swedish Pat. No. 363,193. Air is supplied to thecombined air and electrolyte interspace 28 by means of the channelsystem 29 and is discharged from the upper part of the interspace 28over the overflows 30. End elements 31 are arranged in the two ends ofthe pile, with mono-polar electrodes being connected to the pole bolts32. To make the description easily understood, the figure has beensimplified a great deal with exaggerated dimensions.

If the modification of the prior art battery of FIG. 1, as depicted inFIG. 6, is carried out with electrodes which exhibit a hydrophilicsurface towards the electrolyte, the cell will give comparatively poorload characteristics, also when there is a rich supply of air to thecombined air and electrolyte space. This is due to the fact that theoxygen has to diffuse through a thick electrolyte film on the electrodesurface. Therefore, it is suitable to take measures which have thepurpose to assure the supply of oxygen to the electrocatalyticallyactive material and, at the same time, to maintain a good electrolyteconnection between the two electrodes 23 and 25. These two goals resultin competition for the available volume in the interspace 28 andtherefore a compromise must be made. The anode, that is the porous ironelectrode, should be in contact only with the electrolyte, where as thecathode, i.e., the gas electrode, should be in contact with theelectrolyte as well as air.

The distribution can be described by means of the gas/liquid surfaceratio of the electrode surface. This is the ratio between the electrodesurface which is mainly in contact with gas, and the electrode surfacemainly in contact with liquid. Electrode surface, as used here, meansthe outer geometrical area of the electrode. Surface in contact with gascan be completely or partially covered by an electrolyte film, whereassurface in contact with liquid refers to such surfaces which are indirect contact with the opposite electrode, in this case the anode, bymeans of a continuous electrolyte mass.

Another important geometrical factor is the average distance betweenadjacent points of gas electrodes in contact with gas and liquid,respectively, according to the invention. The electric current must beconducted from the electrochemically active sites on the parts of thecathode which are in contact with gas, to the parts in contact withliquid, the latter being, in turn, connected with the anode viaelectrolyte bridges. The resistance in this current path must be kept onan acceptable level which can be done by minimization of the averagedistance between parts in contact with gas and liquid, respectively.Such distance could preferably be defined by the distance between thepoints of inertia for the surfaces in question and which can be calledthe gas/liquid distance. The resistance in this current path is, ofcourse, also dependent upon the cross section of the current path andthe resistivity of the electrolyte film. The cross section is, amongother things, influenced by the thickness of the gas-diffusion electrode25. Several other factors are of importance for performance and otherproperties of the chemoelectric cells according to the invention, butthese factors do not have the same decisive importance as thosementioned above.

There are several possibilities for controlling the gas/liquid surfaceratio and the gas/liquid distance, from controlled addition of air whichis permitted to rise freely to mechanical means in the interspacebetween the electrodes. It is often of advantage to work with agas/liquid surface ratio which is above 1, a particularly advantageousratio range is 2-5, but also higher values for this ratio are frequentlyuseful, for instance the range 5-20 or above. The gas/liquid distanceshould be as small as possible, preferably below about 1-2 cm, a usefulvalue is below 0.5-1 cm and a particularly useful range is 0.1-0.5 cm orbelow. Short gas/liquid distances permit very thin gas diffusionelectrodes, down to 0.01 to 0.02 cm or below. With higher values for thegas/liquid distance it may be necessary to work with electrodethicknesses within the range 0.4-0.8 mm. A possibility for reducing theresistance in the current path is thereby to dispose anelectrolyte-filled layer adjacent to the electrochemical active andpartially gas-filled layer of the electrode material, whereby the ioncurrent makes its way from the electrolyte film to thiselectrolyte-filled layer in order to be then conducted over to theelectrolyte in the interspace between the electrodes.

There are a large number of possible embodiments of the invention. Thisrichness of alternatives extends partly from the fact that the inventioncan be applied for different kinds of power sources and electrolyzerslike metal air cells, methanol air cells, hydrogen air cells, hydrogenmetal oxide cells, alkali electrolyzers, etc. The different cell typescan, in turn, be built up in different ways, for instance with so-calledmono-polar electrodes or bi-polar electrodes. Chemoelectric cells withtwo gas electrodes, for instance the hydrogen air cell, can be made withthe one electrode according to conventional technic and the other, gaselectrode designed according to the invention; alternatively, with thetwo gas electrodes designed according to the invention. The latterembodiment requires special separators in the interspace since then twogases shall be supplied to the corresponding electrode materials fromthis interspace.

The method to supply gas to the gas electrodes, which is acharacteristic feature of the invention, can be obtained by severaldifferent co-operating measures which, of course, are also influenced bythe cell type in question and other special requirements. These measurescan be described as (1) constructive modifications of the means forsupply and discharge of electrolyte and gas to the interspace, (2) theintroduction of special means like conducting and distributingstructures in the interspace and (3) constructive modifications of theelectrodes for the purpose of facilitating the supply of gas accordingto the invention. These measures can be combined with each other andwith special treatments of the electrode material for the purpose ofmaking parts of its (1) better gas receptive (most frequentlyhydrophobic), (2) electrolyte receptive (hydrophilic) or (3) blocked(sealed) to prevent supply of gas as well as electrolyte to theelectrode parts in question. It is no difficulty for the artisan withthe knowledge of the spirit of the invention to take suitable measuresof this kind and therefore we shall in the following only mention a fewembodiments which are particularly preferred so as to illustrate thepossibilities of these alternative routes. An iron air battery will beinitially described with bi-polar electrodes, according to FIG. 6, whichgives a simple exemplication of the spirit of the invention.

A complication with metal air cells compared to fuel cells is that twomodes of operation are used, that is, charge and discharge. Duringcharge, oxygen is developed in the cell when the active material of themetal electrode is reduced to metal. One may use the air electrode alsofor oxygen development during charge but there are also embodiments,e.g., the so-called third electrode which is used for the oxygendevelopment during charge. The electrode materials which are being usedin air electrodes frequently contain one or several metals which showconsiderable resistance towards oxygen development during charge,whereas other electrodes like platimized and hydrophobic porous carbonstructures deteriorate during charge and therefore require a specialfine layer on the electrode where the oxygen is developed, or a thirdelectrode which is used only during charge.

FIG. 7 shows a simple embodiment of an air electrode seen from one ofthe interspaces 28 in FIG. 6. The dimensions are also in this caseexaggerated for clarity. The cathode surface is intermittentlyhydrophobic and hydrophilic. An originally hydrophilic structure, forinstance, corresponding to the coarse layer of the two-layer electrodemanufactured according to the recommendations in the Swedish Pat. No.360,952, has been made hydrophobic in parallel strips 33 which intermixwith non-treated hydrophilic parts 34. The width of the hydrophobicstrips is, in reality, 0.3 cm and the widths of the hydrophilic ones 0.1cm and, therefore, the distance between the points of inertia of thesurfaces is 0.2 cm.

In operation, electrolyte is supplied via the channels 35 and isdischarged via the overflows 36. Air is supplied via the channels 37 andis vented from the interspace to the surrounding vessel, which is notshown, via the exhaust gas channels 38. In operation, the air willpreferably follow the hydrophobic parts of the cathode, while theelectrolyte will follow the hydrophilic ones. This effect can bemagnified by having also the anode covered with a hydrophobic layer inthe opposite position of the corresponding layer of the cathode. Anotherpossibility is to seal the anode completely on these surfaces by meansof a hydrophobic film of, for instance, polypropylene which can beaccomplished by means of plasma spraying or in other ways. Under theseconditions, the gas/liquid surface ratio is about equal to the ratiobetween hydrophobic and hydrophilic electrode surface, that is, 3.

The hydrophobic strips 33 in FIG. 7 can preferably be obtained by meansof impregnation with Teflon® dispersion, for instance, containing 15%Teflon followed by evaporation and sintering at a temperature around300° C. according to the general technique with hydrophobization ofporous electrode materials, particularly fuel cell electrodes. In orderto produce the geometric pattern desired, the Teflon dispersion can bepainted in corresponding strips. The parts of the electrodes, whichshall remain hydrophilic, may also be protected with a master sheet oralternatively painted with a stripable paint or a protective film whichcan be dissolved in the electrolyte or vaporized during the heattreatment of the material. Another possibility is to press a nickel netor a perforated nickel plate, etc against a hydrophobic ground structurewhereby the net etc will serve as the hydrophilic surface.

FIG. 7 shows for simplicity a pattern with parallel vertical strips. Onemay also visualize many other patterns depending on special requirementsto assure a uniform flow over the whole cross section. FIGS. 8A-8B giveexamples of such useful alternative patterns. Thus, in FIG. 8A, thehydrophobic areas 33A are rectangular with the remainder of the surface34A being hydrophilic. In FIG. 8B, the hydropholic strips 33B arewavelike. In FIG. 8C, the hydropholic areas 34C are rectangular andextend at an angle to horizontal and vertical.

State of the art materials can in general serve very well as theelectrode materials in the iron air cell according to FIGS. 7 and 8. Theiron electrode may thus be made according to the Swedish Pat. No.360,952, as well as the active material of the air cathode. It is,however, useful to apply the catalysts for the oxygen reduction in theair touched strips and catalysts for oxygen development in theelectrolyte touched strips.

Since no differential pressure can be applied, it is necessary to makethe hydrophobization of the cathode material fairly strong. It may alsobe desirable to work with comparatively large pore dimensions and highporosity in the structure. This can be done easily in this case becauseof the small mechanical stresses on the structure. When the requirementsof life are modest, one may also use a Teflon-bonded active carbonstructure containing incorporated and activated nickel nets.

For more qualified purposes with requirements involving higheroperational temperature and charge current, one may use a partiallyoxidized and hydrophobized nickel electrode with catalysts of silver,cobolt or nickel basis. The interspace can be completely open as in FIG.7, or supplied with supports and spacer elements. It may sometimes benecessary to wrap the anode in a separator to prevent direct contactbetween the oxygen of the air and the active anode material.

During charging, oxygen will develop primarily on the hydrophilic partsof the cathode, which preferably are covered with materials like nickelwhich decreases the oxygen overvoltage, whereafter the gas will find itsway over the hydrophobic strips. The very simple embodiment of theinvention according to FIG. 7 gives a surprisingly good technicaleffect. It is not surprising that the oxygen transport will besatisfactory in this way but very much so that ion transport between theelectrodes does not deteriorate too much.

There is no difficulty for the artisan to design a complete system withall necessary functions for this kind of power source on the basis ofthe above description. An important question relates to the distancebetween the electrodes, that is, the width of the interspace which amongother things depends on whether the battery is intended for operation atlow or high current densities. High current densities, of course,require more air which influences the dimensioning of the interspace.The width is in general around 0.2 mm to 2.0 mm. With small distancesbetween the electrodes, it may be useful to introduce special spacerelements which may also be used to control the flows in the interspace.

A comparison between the iron air battery described in the Swedish Pat.No. 360,952 gives the following advantages. The active electrodematerial which may be said to correspond to the composition of thecoarse layer in example 5 may be reduced to 0.2 mm, that is 30% of thereference electrode, which is equivalent to the electrochemically activezone in the material. This reference electrode was dimensioned mainlyfor mechanical reasons. If the thickness of the electrolyte space is thesame in the example of reference, the so-called cell-pitch for a givencapacity will be reduced with about 30%, which corresponds to anincrease of the energy density (per volume unit) with about 40%. Underotherwise comparable conditions, the power density (per unit area) willbe reduced by about 20%, but on the other hand the amount of area whichcarries current will be increased by about 40% per unit volume.Therefore, the power density for the battery has also been improvedconsiderably with the design according to the invention.

It is also obvious that the invention does permit a simple solution tothe difficult problem of designing bi-polar metal air electrodes.Bi-polar electrodes reduce the volume of the battery and its weight,since there will be no need for current conductors. Furthermore, acompletely uniform current distribution over the cross section of thecell will be obtained which means that structures like metal nets,frequently used in iron electrodes for better electronic activity, maybe eliminated which also saves weight, volume and cost.

Another important thing, which is not immediately realized, is that abetter cooling is obtained compared to the state of art. Heat isdeveloped particularly in the cathode material which is now cooledefficiently in direct contact with air and electrolyte, whereby theshort distances prevent thermal spikes in the material. It is thereforepossible to increase the operating temperature compared to cellsaccording to the state of art without a sacrifice in life of the cell.

The beneficial effect on the cooling of the air cathode may also beobserved with mono-polar air elements which are in contact with coolingelectrolyte on both sides, corresponding to the application of theinvention for metal air cells with a principle design according toFIG. 1. The higher operating temperature is of very great importance forperformance and reduces the size of the auxiliary system which is mainlygoverned by the cooling requirements. A useful operation temperature isnow 50°-60° C. compared to 40°-50° C. with the corresponding iron aircells according to the prior state of the art.

A great advantage with gas electrodes according to the invention, whichis of particularly great importance with air electrodes, is that the gaswill take up moisture very fast in the direct contact with theelectrolyte. With air electrodes according to the prior state of theart, such humidification will also take place in the air space (providedthat the incoming air is not already saturated with moisture). In thiscase the moisture will be taken up from the electrolyte in the gasdiffusion electrode which frequently leads to local drying out,particularly near the air inlet to the air space. Such local drying outwill, in turn, cause severe corrosion damage which produces localconstrictions in the air space. Metal air batteries according to theprior state of the art therefore require that the air be moistenedbefore entrance into the air spaces, or special corrosion-preventivemeasures be taken in the air electrode itself. One consequence of thecircumstances discussed above is that the cathode can be loaded harder,for instance during operation on pure oxygen, or during operation atincreased pressure on oxygen and/or oxygen air mixtures. This is ofinterest in special applications like pressurized iron oxygen batteriesfor submarine propulsion. Gas electrodes according to the invention canalso be utilized harder under extreme conditions than what is possibleaccording to the prior state of the art thanks to the better conditionsfor heat transfer.

After this presentation of a very simple possible embodiment of theinvention, whereby I have discussed the advantages of the invention, Ishall now describe more complicated embodiments which require specialmeasures and means in the interspace and in the electrodes. FIG. 9 showsan embodiment with a special structure 39 disposed in the interspace 28which governs the flows of gas and electrolyte in a more controlledmanner. FIG. 9 shows several separate features and one or more of theseneed not be used in less demanding applications. FIG. 9 shows a crosssection through the electrodes and interspace, as seen from above,whereby for simplicity the gas and electrolyte flows are arrangedvertically as in FIGS. 6 and 7. (The dimensions are also exaggerated forthe sake of clearness). The structure 39 can be manufactured from aconventional separator material which has been compacted and eventuallyfurther sealed by impregnation or welding in the surface portions 40 andpossibly also in the side surfaces 41. Separator materials which areuseful for alkaline systems are described in Alkaline Storage Batteriesby U. Falk and A. Salkind, particularly the pages 26, 28, 70, 140, 142,168, 178, 202, 240, 243, 246 and 349. This will give a straight gaschannel 42 which supplies gas to the hydrophobic strips 33 on the airelectrode. Electrolyte is supplied via channels or traces 43 and isdistributed in the porous electrode material 34. Channels 44 are alsoprovided in the anode for electrolyte transport.

During charging, oxygen is developed primarily in the channels 43. Sideconnections can also be arranged between the electrolyte channel 43 andthe air channel 42 to make oxygen pass over to this channel.

As has been mentioned above, several of these features may be dispensedwith and others may be added. With respect to electrolyte circulation,there exists a possibility to arrange internal circulation with thechannels 44 in the anode and the channels 43 as down-comers, andeventually the air channel 42 as risers (electrolyte would here be addedthrough the air channel 42).

The embodiment with specially formed channels in the interspaceaccording to FIG. 9 makes possible a variation of the airflow withinwide limits. Furthermore, this will give a good separation between theelectrodes, which reduces risks for short circuits.

There are obviously many variations of the embodiment which was shown inprinciple in FIG. 9. One such possibility is to arrange the channels inthe iron electrode as shown in FIG. 10. Channels 45 have been heredisposed in the anode 23, which are eventually sealed for instance bypainting or welding of a plastic film. Electrolyte contact between theelectrodes can be obtained by means of free electrolyte film orelectrolyte-filled porous separator columns 46.

FIG. 11 shows a variation with profiles of plastic 47 in channels 48which simultaneously serve as spacer elements between the electrodes,and which divide liquid and gas-touched parts. These inlets can bemanufactured of polystyrene or other suitable polymeric material.

FIG. 12 shows a coherent structure which is composed of a thin bottomfoil 49 supplied with holes 50 adjacent the electrolyte conductingchannels 52. The adjacent channels, defined by wings 51, conduct air.The space 52 can, with advantage, be filled with porous electrolyteabsorbing separator materials, whereby the electrolyte circulation ispreferably obtained by means of channels 44 arranged in the anode.

Simple flow patterns have been used in the above examples for the ironair battery used as an example. Air is supplied to the lower parts ofthe interspace and is vented in its upper part. The electrolyte, inprinciple, follows the same path in the interspace.

The invention is, of course, not limited to these special flow patterns.There are different possibilities for controlling gas flow as well aselectrolyte flow. For instance, supporting structures and dividerelements can extend diagonally from one inlet channel to an outletchannel. Quite different embodiments, like zig-zag flows or spiral flowsfor gas as well as liquid, are also possible.

The electrodes do not need to be essentially planar as shown in thefigures. Electrodes may thus be corrugated to a wave shape so as toincrease the electrode surface in the given cell volume. The electrodemay also contain wings of the electrode material, the edges of whichcontact the electrolyte phase. Plain electrode systems can also berolled to cell cylinders which may be contained in cylindrical cellvessels. Hybrid forms are also possible utilizing features from theprior art and the present invention.

FIG. 13 shows such an example with a self-respirating metal air cellseen in cross section from above. The metal electrode 23 is wrapped in aporous separating and electrolyte-impregnated structure 53 (which inprinciple corresponds to the structure 39 in FIG. 9) having channels 42.The cathode material 25, which can be Teflon-bonded active carbonsupported by a thin nickel-coated iron net 54 and protected with aporous foil of polyethene 55, is wrapped around the metal electrode. Aircomes in contact with the electrode material as well as from theinterspace on the outside according to the invention as well as from theoutside according to the state of art for self-respirating metal aircells.

FIGS. 14-15 show a cylindrical iron air battery, which may replaceconventional so-called dry cells, consisting of two iron air cells whichhave been joined in series by means of a bi-polar iron air electrode.The negative pole 56 of the battery is connected to the central porousiron air electrode 57 which is surrounded by an electrolyte-impregnatedseparator 58 having air channels 59 for the supply of air according tothe invention. The cathode material 60 is arranged on the plate 61which, in turn, carries a layer of porous iron 62. These threecomponents 60, 61, and 62 constitute a bi-polar iron air electrode.Thereafter there is another layer of electrolyte-impregnated separatormaterial 63 having air channels 64 which face the cathode material 65arranged on the cylinder 66 which is connected to the positive pole 67of the battery.

FIG. 14 shows the battery body proper with the components 57-66 in crosssection seen from above. FIG. 15 shows a cross section through thecomplete battery seen from the side, with the battery body 68 beingconnected to the two poles 56 and 67 and contained in an isolatingcylinder of plastic. Spaces 70 and 71 are arranged in the upper andlower part of the cylinder, which spaces serve for the supply anddischarge of air to and from the channels 59 and 64. These spacescommunicate with the surrounding atmosphere by means of holes 72 and 73which may be arranged as in FIG. 15 in the mantel surface of thecylinder. The holes can be locked by means of movable rings 74 and 75which are supplied with holes 76 and 77 corresponding to the holes 72and 73 in the periphery of the cylinder. Air may, of course, be suppliedin an analogous manner via the top and the bottom of the battery. It isno difficulty for the artisan to manufacture a battery according to thisdescription and by means of the technology which has been developed forzinc air cells, alkaline manganese dioxide elements, cylindricalnickel-cadmium batteries, etc. The iron air battery according to FIGS.14 and 15 has an energy density of several hundreds Wh/kg. isrechargeable, and is manufactured of inexpensive materials which do notconstitute a nuisance to the environment, and therefore represents animportant step forward compared to the battery types now in use. Thebattery may also be made in larger sizes, for instance, tractionalapplications.

The above description has, for simplicity, been made in relation to ironair batteries of different kinds for the purpose of illustration. Thesame technique can be used for cadmium air batteries of different kindsas well as for zinc air batteries. The state of the art with respect tomethods for the manufacture of these electrodes, useful separators, etcis well described in the book of Falk and Salkind referred to above.With respect to the zinc electrode, a special reference can be given tothe book Zinc-in-Alkali Batteries by R. V. Robker, published by TheSociety for Electrochemistry in England, August 1973. Zinc air systemsare complicated by the fact that the zinc electrode goes completely orpartially into solution during discharge. This does, however, notproduce special problems for the application of the present invention.On the contrary, it has been shown that problems with the zincelectrode, that is, shape change and dendrite growth, are solved in abetter way with air electrodes according to the invention. This dependsprobably on the uniform current distribution and the means in theinterspace between the electrodes which also seem to prevent dendritegrowth.

It is also no difficulty for the artisan to use the invention for othertypes of power sources which use gas electrodes. The examples may thusbe applied directly also to hydrogen nickel oxide batteries whereby thenegative metal electrode is replaced with a positive nickel oxideelectrode and the positive air cathode with a negative hydrogenelectrode.

One may, of course, also replace the nickel oxide electrode with otherpositive electrode materials which are used in alkaline systems, likesilver oxide, mercury oxide or iron oxide. Furthermore, the examples canbe applied to methanol air batteries if the metal electrode is replacedwith a methanol electrode of porous nickel with noble metal catalysts ofcommon type. One modification of this embodiment is that the carbondioxide produced is vented through channels in the electrode by means ofpH-gradients in the electrode. It may thereby be useful to minimize thecontact between the electrolyte and air cathode, whereby the parasitingoxidation of methanol is reduced by means of sealing as shown in FIG. 9.Methanol may preferably be added to the methanol electrode by channelscorresponding to the channels 44 in FIG. 9.

The invention may also be used with power sources like hydrogen aircells where the two electrodes are gas electrodes. One simple form ofsuch embodiment is a combination of a conventional electrode accordingto FIG. 1 which may, for instance, be fed with hydrogen produced byreforming of methanol or hydrocarbons, whereby the positive electrodecan be an air electrode of the same kind as described above. Thehydrogen electrode is separated from the air electrode and an interspaceaccording to the invention for the supply of air to the air electrodefrom this interspace.

FIG. 16 shows a hydrogen air battery with both hydrogen and the airelectrodes designed according to the invention. In this case, hydrogenand air flows are separated from one another in the electrolyte space bymeans of an electrolyte-filled separator 78 which, at the same time,serves as a guiding element for the respective gas flows in contact withthe electrodes. Air is supplied to the electrodes 25 via the pipingsystem 29 and is vented via the piping system 30. Hydrogen is suppliedan analogous manner to the electrodes 23 via the piping system 79 and isconducted away via the piping system 80. Other necessary structure, forinstance, to provide electrolyte circulation, etc are not shown.

Quite large requirements are, of course, put on the separator 78 whichmust prevent hydrogen and air from coming into contact with each otherand it is therefore useful to make this separator in several differentlayers. The separator may also contain a sheet of sintered porous metalin order to improve further the mechanical stability. The separator mayalso contain channels for electrolyte supply and discharge to assure thesupply of electrolyte to the gas diffusion electrodes.

FIG. 17 shows a chlor alkali electrolyzer according to the inventionhaving an air electrode 25 arranged in the catholyte space 12 accordingto the invention. A corresponding alkali electrolyzer with hydrogenanode 23 according to the invention is shown in FIG. 18. FIG. 18 showsan alkali electrolyzer with both a hydrogen electrode 23 and an airelectrode 25 according to the invention. For more details concerning theconstructive design of this electrolyzer, see U.S. Pat. No. 3,864,236.It is not difficult for the artisan to design chlor alkali electrolyzersand alkali electrolyzers according to the invention with the knowledgeof this patent and, for instance, U.S. Pat. Nos. 3,124,520 and 3,262,868and the description above. It is of particular advantage to modifybi-polar designs like the GLANOR® electrolyzer with air cathodesaccording to the invention. The technology in this field is welldescribed for instance in the Monograph No. 154, "Chlorine," publishedby the American Chem. Soc.

The present invention is of a general character and can be applied forall kinds of chemoelectric cells where gas diffusion electrodes are usedin contact with an electrolyte. The invention is, of course, not limitedto the embodiments which have been described above but can also beapplied for all kinds of chemoelectric cells with gas electrodes. Thespirit of the invention is very simple as is apparent from the abovedescription. To realize the technical effect possible, special measuresare required which vary from case to case. There is, however, no problemfor the artisan to transform the spirit of the invention to operablechemoelectric cells applying known technology in each such case.

Although the invention has been described in connection with preferredembodiments thereof, it will be appreciated by those skilled in the artthat additions, modifications, substitutions and deletions notspecifically described may be made without departing from the spirit andscope of the invention as defined in the appended claims.

What is claimed is:
 1. A chemoelectric cell comprising:a positiveelectrode, a negative electrode spaced from said positive electrode todefine an interspace therebetween for conducting electrolyte,one of saidelectrodes comprising a gas electrode having one side facing saidinterspace, a porous separator disposed in said interspace and abuttingagainst said side of said gas electrode,said separator definingpassageways open toward said side of said gas electrode for conductinggaseous substance from an inlet end to an outlet end of said interspace;portions of said side of said gas electrode located along saidpassageways being coated with electrolyte repellant material, means fordelivering electrochemically active gaseous substance into saidpassageways for travel along and reaction with said portions of saidside of said gas electrode that are coated by said electrolyte repellantmaterial, and means for delivering liquid electrolyte to said interspaceto impregnate said separator so that electrolyte is in contact withareas of said side of said gas electrode which are abutted by saidseparator.
 2. A chemoelectric cell according to claim 1 wherein theratio between the areas coated with electrolyte repellant material andthe remaining areas of gas electrode surface is in the range of 5-20. 3.A chemoelectric cell according to claim 1 wherein the average distancefor the current path between said electrolyte repellant and remainingareas of the gas electrode is no greater than about 1-2 cm.
 4. Achemoelectric cell according to claim 1 wherein the average distance forthe current path between said electrolyte repellant and remaining areasof the gas electrode is no greater than about 0.5-1 cm.
 5. Achemoelectric cell according to claim 4, wherein said distance is withinthe range 0.2-0.5 cm.
 6. A chemoelectric cell according to claim 1wherein the negative electrode material is iron and the gas electrode isan air electrode.
 7. A chemoelectric cell according to claim 1 whereinthe positive electrode material is zinc and the gas electrode is an airelectrode.
 8. A chemoelectric cell according to claim 1 wherein thenegative electrode material is cadmium and the gas electrode is an airelectrode.
 9. A chemoelectric cell according to claim 1 wherein thenegative electrode material is zinc and the gas electrode is a chlorineelectrode.
 10. A chemoelectric cell according to claim 1 wherein thenegative electrode is a hydrogen electrode and the positive electrodematerial is nickel oxide.
 11. A chemoelectric cell according to claim 1wherein the negative electrode is a hydrogen electrode and the positiveelectrode material is iron oxide.
 12. A chemoelectric cell according toclaim 1 wherein the negative electrode is a hydrogen electrode and thepositive electrode is an air electrode.
 13. A chemoelectric cellaccording to claim 1 wherein the negative electrode is a methanolelectrode and the positive electrode is an air electrode.